Concrete is a tension-weak building material which often cracks under low load levels of tensile stress. The cracks generally develop with time and stresses to penetrate the concrete to destructive substances. It has been recognized that the behavior of concrete can be improved by reinforcing it with discontinuous fibers. The concrete reinforcing fibers include metal, polymer, glass, carbon etc.
Among the polymer fibers the polypropylene fibers have become popular in recent years due to their effectiveness in reducing cracking at early ages under the effects of restrained plastic shrinkage, easy handling and lower costs compared to other types. Plastic shrinkage cracks are most common on horizontal surfaces of pavements and slabs where rapid evaporation occurs and its occurrence destroys the integrity of the surface and reduces its durability.
An increasing amount of plastic waste is a worldwide problem which has led to requirements for its recycling and reuse of such materials. For example, polyethylene terephthalate (PET) is a thermoplastic polymer resin of the polyester family commonly used to make PET bottles used as beverage containers. Such containers are thrown away after a single use and disposed bottles are managed by landfill and incineration which cause environmental problems. Therefore, recycling holds promise for returning the waste into service and promotes the use of such materials in construction.
The development of new construction materials using recycled plastic is important to both the construction and plastic industries. This has led to an increase interest in the use of recycled plastic fibers or strands as a secondary reinforcement in concrete since they are generally considered to be non-biodegradable and may not need to be purified and separated to the same extent as recycled plastic used in other applications. Therefore, manufacturing recycled plastic fibers or strands from industrial or post-consumer waste should offer effective reinforcement of concrete and an additional advantage of waste reduction and resource conservation.